docs: add Svix to showcase (#7254)

* docs: add Svix to showcase

Motivation
Svix uses Docusaurus for our documentation. It could be cool to add it in the showcase page.

Have you read the Contributing Guidelines on pull requests?
Yes

Test Plan
Run yarn run start:v2 and check that the page http://localhost:3000/showcase is rendered properly.

Related PRs
No

* Add svix doc preview image

* Delete Svix.png

* re-upload preview image

needed to make file name lower case.

* optimize image

Co-authored-by: Joshua Chen <sidachen2003@gmail.com>

website/src/data/users.tsx

@@ -1801,6 +1801,14 @@ const Users: User[] = [
     source: 'https://github.com/supabase/supabase/tree/master/web',
     tags: ['opensource', 'favorite', 'design', 'large', 'product'],
   },
+  {
+    title: 'Svix',
+    description: 'Webhooks as a Service',
+    preview: require('./showcase/svix.png'),
+    website: 'https://docs.svix.com/',
+    source: 'https://github.com/svix/svix-docs',
+    tags: ['opensource', 'product'],
+  },
   {
     title: 'Synergies',
     description: